Approximately 68% of a normal distribution lies within one standard deviation of the mean, so this corresponds to students with scores between (57.5 - 6.5, 57.5 + 6.5) = (51, 64)

Explanation:
Since we have given that
The prices of three t-shirts styles i.e $24, $30, $36 with their probability is given by

As we know that,


Now,

and

So,

So, the expected value of a t-shirt = $31.
We know that
A barber shop produces 96 haircuts a day----------> <span>8 hours per day
so
96/8--------> 12 haircuts per hour
if </span><span>if the shop's productivity is 2 haircuts per hour of labor
then
12/2---------> 6 </span><span>barbers
the answer is
6 </span><span>barbers</span>